New drugs are being synthesized and tested as inhibitors of cholinergic neurotransmission in Schistosma mansoni. The drugs are mostly analogs of a one-armed acetylcholine mustard; some phenothiazine derivatives will also be tested. The effects of these drugs on schistosomes will be assessed by activity monitoring and by measurements of acetylcholinesterase inhibition. Parallel studies will be conducted with verebrate tissues, such as guinea pig ileum and frog rectus abdominus; bovine erythrocyte acetylcholinesterase will be used for enzyme studies. The relative activity of the new drugs on the schistosome and the vertebrate preparations will be measured, and further plans for drug synthesis will be made according to those structures which produce the most advantageous selectivity.